HR: 0800h
AN: T11B-0372    [Abstracts]
TI: Double Indenters and Oblique Extrusion and Extension in Taiwan: the Colliding Seamount Analogy
AU: * Byrne, T
EM: tim.byrne@uconn.edu
AF: Center for Integrative Geosciences, University of Connecticut 354 Mansfield Rd, Storrs, CT 06269 United States
AU: Gourley, J R
EM: jonathan.gourley@uconn.edu
AF: Center for Integrative Geosciences, University of Connecticut 354 Mansfield Rd, Storrs, CT 06269 United States
AU: Chan, Y
EM: yuchang@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academic Sinica 128 Academia Road, Sec 2, Nankang, Taipei, 115 Taiwan
AB: The island of Taiwan forms as the ENE-trending Chinese continental margin collides obliquely with the N-trending Luzon arc. Previous interpretations have treated the colliding margin as a relatively homogeneous basement high with lateral extrusion limited to southwestern Taiwan. Here, we present a new compilation of geologic, GPS and seismic data and propose that the collision can be more accurately represented as a series of colliding indenters, similar to the subduction of seamounts, and that lateral extrusion affects nearly the entire collision. The most recent indenter, the Peikang basement high, lies beneath the southern Coastal Plain and has been mapped through drilling and seismic reflection and refraction studies. The high is generating a prominent reentrant in the deformation front in the Coastal Plain and correlates arcward (in the direction of plate convergence) with a substantial increase in GPS measured shortening, the maximum elevation in Taiwan (3952 m), a slightly wider retro-wedge, and the area where the emerging colliding arc is highest and widest. A second, previously accreted, basement indenter appears to lie beneath the slate and pre-Tertiary metamorphic belts in the Central Range and lies at the apex of a second topographic reentrant east of the Puli Basin. The indenter also correlates arcward with an increase in GPS measured shortening and with an anomalous zone of shortening, rather than extension in the Central Range. A significant cluster of post-Chi-Chi earthquakes defines a steep, WNW-dipping reverse fault in the middle crust (15 to 30 km) that marks the western side of the indenter. This fault probably correlates with the eastern side of the Hsuehshan Range "popup" and with the Lishan fault. The compilation of data also suggests that the fold-and-thrust belt, Slate Belt and pre-Tertiary metamorphic basement are being extruded and extended obliquely as the indenters collide. Extrusion and extension are oblique because the plate convergence vector is about 20° cw to the plate boundary normal and because the South China Sea and Okinawa Trough regions provide significant gradients in gravitational potential energy. North of the indenters, extrusion and extension of the pre-Tertiary metamorphic basement is accommodated on its western margin by slip on a left-lateral normal shear zone (Gourley and Byrne, 2005). South of the indenters, extrusion of a wide region of the fold-and-thrust belt, Slate Belt and pre-Tertiary metamorphic basement appears to be accommodated by several oblique slip right- and left-lateral faults and a wide zone of left-lateral extension in the eastern Central Range.
DE: 8000 STRUCTURAL GEOLOGY
DE: 8015 Local crustal structure
DE: 8104 Continental margins: convergent
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005